The experience at the Cleveland Clinic from 1982 to 1990 using thrombolytic therapy for superior vena cava (SVC) syndrome was retrospectively reviewed. Sixteen patients, 11 of whom had indwelling central venous catheters, were treated with either urokinase (n = 11) or streptokinase (n = 5). Either urokinase (4,400 U/kg bolus followed by 4,400 U/kg/h) or streptokinase (250,000 U bolus followed by 100,000 U/h) was used, and venograms were performed before and after. Overall, 56 percent of patients had complete clot lysis and relief of symptoms. Thrombolytic therapy was effective in eight (73 percent) of 11 patients receiving urokinase and one (20 percent) of five patients receiving streptokinase. Of those with a central venous catheter, eight (73 percent) of 11 patients were successfully lysed, whereas only one (20 percent) of five patients was successfully lysed if no catheter was present. If thrombolytic therapy was performed less than or equal to five days of symptom onset, seven (88 percent) of eight patients were successful, if thrombolytic therapy was performed greater than five days after symptom onset, two (25 percent) of eight patients were successful. Symptoms were relieved and the catheter was preserved in patients in whom thrombolytic therapy was effective. Factors predicting success were as follows: (1) the use of urokinase compared with streptokinase; (2) the presence of a central venous catheter; and (3) a duration of symptoms less than or equal to five days.